#5 Only 32 bytes are shown



I try to reverse engineer a usb-token with the help of
SnoopyPro version 0.22. Whenever I send a command
that is longer than 32 bytes the trace is cut to these 32
bytes. I am not sure whether it is the fault of
SnoopyPro, the application or anything else, but I
thought you might know what the problem could be.

Here is a command that was cut at the 32'st byte:

0000: 00 20 20 00 da 01 6e a5 83 02 20 b1 85 08 22
0010: 0c 00 ff ff 00 00 86 07 00 00 00 00 00 00 00 8b
0020: 10 ff ff b9

The lenght byte of the header ( 3rd byte ) says that the
buffer has 0x20 bytes but the lenght of the command
says that there will 0xa5 bytes follow ( 8th byte ). And
indeed the command was cut at the 0x20th byte.

Maybe you know what the problem could be, or mybe I
have just missed something important ?




  • Fabian Melzow

    Fabian Melzow - 2002-10-17

    Logged In: YES

    There is a maximum packet size for each usb endpoint, you can
    only send packets of this size at once. The maximum packet
    size can be found in the endpoint description. You must transmit
    your data in 32 byte chunks and it should work.

  • Nobody/Anonymous

    Logged In: NO

    I have realized that larger data is transmitted split up in
    serveral packets of 32 bytes size. But it seems that
    SnoopyPro does not display several packets belonging to one
    command properly. Is sometimes mixes up the direction of
    the packages and *seems* to display the same data twice.
    But now I have found out how to read the output of SnoopyPro
    and therefore it is'n a problem anymore ( at least for me ... )




Log in to post a comment.

Get latest updates about Open Source Projects, Conferences and News.

Sign up for the SourceForge newsletter:

JavaScript is required for this form.

No, thanks